Virtualization of networks and computers is a reality today. One prominent example for computer virtualization, which can be utilized by more or less anyone, is the Amazon Elastic Compute Cloud (Amazon EC2). It is a web service that provides dynamic computer capacity to their customers. Also, computer virtualization is common in data centres where resources can be shared in order to increase utilization of hardware. Developed prototypes running in virtualized environments have been described in the document “Managing Virtualized Systems—Pinpointing performance problems in the virtual infrastructure, Bernd Harzog, April 2008”. Several virtualization implementations exist including VMWare, see “http://www.vmware.com/”, Sun VirtualBox, see “http://www.virtualbox.com” and XEN, see “http://xen.org/” [2010-01-14].
FIG. 1 belongs to the prior art and discloses a simple example of a virtualized computer. Instead of running one operating system on top of the hardware, a hypervisor 2 runs as a middleware between the operating systems 5 and the hardware 3. The hypervisor acts as a hardware controller that manages the shared hardware recourses among the virtual machines (in which operating systems can run). Application 4, such as for example a web server, represent server software that can be run by a virtual machine. The main intent of the hypervisor is to instantiate the virtual machines, provision the resources and make sure that the resources are shared in a manner decided by an operator, among the executing operating systems. The operating systems depicted in FIG. 1 can be anything ranging from ordinary servers (e.g. Linux running an Apache web server) to software-based routers and switches. This provides a very flexible platform for performing various tasks.
One fundamental problem with respect to virtualization of networks and computers is how to manage the shared resources as well as how to handle dynamic changes in the provisioning, see “Challenges in Resource Allocation in Network Virtualization, Aun Haider and Richard Potter, in 20th ITC Specialist Seminar, May 2009, Vietnam”. Another important issue to address is performance management. For example, performance management tools that are used today do not work satisfactory in a virtualized environment. It is elaborated on this issue in “Timekeeping in VMware Virtual Machines, VMware Inc., 2008” and “Managing Virtualized Systems—Pinpointing performance problems in the virtual infrastructure, Bernd Harzog, April 2008”.
Network communication between a virtual machine on top of a hypervisor and an outside client can of course experience congestion. In the virtualized world the congestion or in other words, the observed network performance degradation, can originate from either real congestion on the physical network outside the physical computer or due to poor resource allocation and sharing of the common resources within the physical computer.